The data
The data used in this study is derived from eight patients with bipolar disorder whose mood was monitored over a period of 5 years. The mood data is returned approximately each week and comprises answers to standard self-rating questionnaires for depression and mania. We restrict the investigation to the depression data which is more amenable to analysis than mania: for some patients, the mania scores are at or near zero for the period of monitoring. The rating scale used for depression is the Quick Inventory of Depressive Symptomatology - Self Report (QIDS-SR16) ([Rush et al. 2000]) which covers nine symptom domains for depression (DSM-IV-TR) ([American Psychiatric Association 2000]). This scale has been evaluated for psychometric properties and found to have high validity ([Rush 2003]). Each domain can contribute up to 3 points giving a total possible score of 27 on the scale. Details of the selection process are given in Additional file 1: Section I and plots of the selected time series are shown in Figure 1.